Device for electrowinning europium with channeled cell and method thereof

ABSTRACT

Disclosed are a device for electrowinning europium and a method thereof. The device for electrowinning europium using a channeled cell including a cathode cell includes a channel having an inlet and an outlet; an anode cell including a channel having an inlet and an outlet; and an ion-exchange membrane tightly interposed between the cathode and anode cells, wherein reduced europium is exhausted from the outlet of the cathode cell.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119 of KoreanPatent Application No. 10-2013-0060319 filed on May 28, 2013 in theKorean Intellectual Property Office, the entirety of which disclosure isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to a device for electrowinning europiumand a method thereof. More particularly, the present invention relatesto a device for rapidly electrowinning europium using a channeled celland a method thereof.

2) Background of Related Art

First, europium (Eu) subject to electrowinning in the present inventionwill be described. Since the Eu is one of rare metals, a general schemeof electrowinning the Eu will be additionally described.

The rare metals refer to metallic elements which have features ofscarcity due to a tiny amount of deposits and localization because therare metals are exclusively concentrated on specific regions, so therare metals are subject to the danger of early exhaustion and areunstable even in supply. In Korea, the rare metal becomes a generic termto refer to 35 kinds of elements such as Li, a rare earth element andIn.

The rare earth element, which is a generic term to refer to total 17elements of scandium (Sc), yttrium (Y) and fifteen lanthanides, has beenused as a core material in phosphor (TV, fluorescent lamp), an abrasive(semiconductor, display) or a permanent magnet (electric vehicle, windturbine).

As describe above, since the rare metal has the feature of scarcity andlocalization, China is a powerful nation in terms of reservation andproduction of the rare elements.

Specifically, since the physical and chemical properties of the rareearth elements are similar with each other, the rare earth elementscould not be refined into the pure elements until the 1990's, so thatthey are rarely utilized. However, recently, as the technique ofseparating the rare earth elements has been developed, the utilizationof the rare earth elements is abruptly increased from 1950.

Conventionally, schemes of separating and extracting a rare earthelement include fractional crystallization, fractional precipitation,selective oxidation-reduction, ion exchange, solvent extraction, andextraction chromatography.

Hereinafter, an electrowinning scheme, which is an ion exchange schemeto separate europium (₆₃Eu) from among various rare earth elements, willbe described.

The europium is an element used for CRTs and three-wavelengthfluorescent lamps as an activator of red phosphor in the form ofhigh-purity oxide so that the demand of the europium has been increased.

However, in spite of the increasing of the demand, the content of theeuropium contained in a rare earth element mineral is less than 0.5%based on all rare earth elements. Thus, a process having several stagesis required for high-purifying the europium.

Until the 1940's to 1950's, the intermediate concentrate containing8˜13% of europium has been obtained through a precipitation or ionexchange resin scheme. After the 1960's, the concentrate containing 75%of europium has been produced through solvent extraction. To obtainhigh-purified europium from the intermediate concentrate, the europiumproperty, in which Eu³⁺ can be easily reduced into Eu²⁺, is utilized.

In detail, the Eu²⁺ loses a property of trivalent rare earth element ionand represents a property of alkaline earth metal ion. Based on theabove property difference, the europium may be easily separated from therare earth elements.

The metallic reduction and electrowinning have been used to reduce Eu³⁺.As describe above, in the present invention, the description of themetallic reduction will be omitted and the electrowinning of europiumwill be described.

First, as electrowinning, Hg-cathode electrowinning will be describedwith reference to FIG. 12 in which an Hg-cathode electrowinning deviceis depicted.

The Hg-cathode electrowinning, which is used first to refine europiumthrough the electrowinning, uses Hg as a cathode and Pt as an anode intwo electrolytic baths connected to each other through a salt bridge.

In detail, according to the electrowinning, the europium concentratecontaining SO₄ ²⁻ ions is put in a cathode bath and sulfuric acidsolution having the concentration of 1 mol/L is put in an anode bath.Then, if electrolyzed, EuSO₄ precipitate is formed by the europium inthe cathode bath.

However, the Hg-cathode electrowinning can process only a small quantityand cause bad purity of europium, and in addition, may cause mercurycontamination when europium oxide is produced, so the Hg-cathodeelectrowinning is not industrially used in recent years.

Next, as an electrowinning scheme, an ion-exchange membraneelectrowinning scheme will be described with reference to FIG. 13 whichschematically shows an ion-exchange membrane electrowinning device.

The ion-exchange membrane electrowinning scheme, which had beendeveloped in 1980's, uses porous carbon electrodes installed in anelectrolytic bath divided by an ion-exchange membrane.

According to the ion-exchange membrane electrowinning, europium iselectrowinning while FeCl₂ solution is being input to the cathode bathat a predetermined speed in the state that concentrated europium (RECl₂,specifically, Eu³⁺) solution is put in the cathode bath.

In this case, the primarily reduced solution is secondarily reduced inan electrolytic bath having the same structure as that of the primaryreduction, so that the europium reduction rate is increased to 99% ormore. Then, the Eu²⁺ solution is transferred into a precipitationdevice.

In the precipitation device, the Eu²⁺ solution transferred from theelectrolytic bath reacts with the mixing solution of ammonium sulfate of2 mol/L and sulfuric acid of 1 mol/L to obtain EuSO₄ precipitate. Then,the europium is separated from the EuSO₄ precipitate. In this case, torestrain europium oxidation due to air contact, the EuSO₄ precipitate ispreferably purged with nitrogen gas.

Next, porous carbon electrode electrolytic reduction will be describedwith reference to FIG. 14 which schematically shows a porous carbonelectrode electrolytic reduction device.

In FIG. 14, reference numerals 1 and 3 denote outlets, reference numeral2 denotes a gas exhaustion hole, reference number 4 denotes an inlet,reference number 5 denotes a glass reaction container, reference numeral6 denotes a cathode, reference numeral 7 denotes an anode, and referencenumeral 8 denotes porous graphite.

Similar to the ion-exchange membrane electric reduction, although theporous carbon electrode electrolytic reduction using the porous carbonelectrode electrolytic reduction device depicted in FIG. 14 uses aporous carbon electrode, the porous carbon electrode has holes smallerthan those of the ion-exchange membrane electrolytic electrode. In thiscase, the porosity is about 43%.

The porous carbon electrode electrolytic reduction utilizes theprinciple that, when the solution containing europium-concentrated rareearth chloride and Br is input to the material inlet under a pressure,the europium reduction reaction occurs while the solution passes throughthe air gaps of the cathode and the oxidation reaction of Br occurs atthe anode.

However, the porous carbon electrode electrolytic reduction also has alow reduction rate so that the recovery rate is deteriorated. Inaddition, the product is contaminated by Br.

As described above, according to the conventional electrowinningschemes, there is adopted a scheme of increasing a reaction area, inwhich a stirrer such as a propeller is used or the reduction bath itselfis rotated in order to increase the quantity of reaction and thereaction speed, or a scheme of increasing a reaction time, in which, asthe ion-exchange membrane electrolytic reduction described withreference to FIG. 13, the electrowinning solution obtained through aprimary electrolytic reduction is secondarily electrolytically reduced,has been used.

There is a related art which is Korea Unexamined Patent Publication No.10-1997-0006187 (published on Feb. 19, 1997) entitled “a method oftreating waste fluid using electrolytic oxidation and apparatusthereof”.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve the aboveproblems, and an object of the present invention is to provide a devicewhich is capable of greatly increasing a reaction quantity of europiumby increasing the contact area of an electrowinning solution containingeuropium ions, and at the same time, reducing a reaction time of theeuropium by increasing a reaction speed of the europium, without using astirring unit and a porous electrode, without rotating an electrolyticbath and without performing a process of electrowinning several times,and a method thereof.

Another object of the present invention is to solve a problem ofcontaminating a target metal, that is, europium (Eu) which occurs in therelated art.

The present invention suggests several objects without limitation to theabove objects, and other objects, which are not described, can beclearly comprehended from the following description by those skilled inthe art.

To achieve the above-described objects, according to an embodiment ofthe present invention, there is provided a device for electrowinningeuropium using a channeled cell including a cathode cell including achannel having an inlet and an outlet; an anode cell including a channelhaving an inlet and an outlet; and an ion-exchange membrane tightlyinterposed between the cathode and anode cells, wherein reduced europiumis exhausted from the outlet of the cathode cell.

Preferably, the cathode and anode cells include graphite.

Preferably, at least one bead for generating a turbulent flow is formedon each inner surface of the channels of the cathode and anode cells.

In addition, a sectional shape of the channel may be one of arectangular shape, a U-shape, and a V-shape.

Preferably, an electrowinning solution input to the inlet flows atReynolds number of 2000 or more.

Preferably, a quantity of electric charge applied to the cathode andanode cells is 110% or more when the quantity of electric charge issubstituted into a value obtained by dividing a quantity of appliedelectric charge by a theoretical quantity of electric charge.

According to an embodiment of the present invention, a solutioncontaining Eu³⁺ is input to the inlet of the cathode cell, and asolution containing Fe²⁺, which is able to pair-react with the solutioncontaining Eu³⁺ input to the cathode cell, is input to the inlet of theanode cell.

Further, at least one bead for generating the turbulent flow isinstalled per a unit length of the channel.

To achieve the above-described objects, according to another embodimentof the present invention, there is provided, a method of electrowinningeuropium using a channeled cell including preparing a substrate for acathode cell and a substrate for an anode cell; forming channels in thesubstrates; fixing the substrates having the channels to both sides ofan ion-exchange membrane by closely attaching the substrates to bothsides of the ion-exchange membrane; and electrowinning europium afterinputting a solution containing an europium ion through an inlet formedin the substrate.

Preferably, the substrate includes graphite.

In addition, at least one bead for generating turbulent flow is formedon an inner surface of the channel of the substrate.

Further, an electrowinning solution input to the inlet flows at Reynoldsnumber of 2000 or more.

In addition, a quantity of electric charge applied to the cathode andanode cells is 110% or more when the quantity of electric charge issubstituted into a value obtained by dividing a quantity of appliedelectric charge by a theoretical quantity of electric charge.

The details of other embodiments are described in the detaileddescription and shown in the accompanying drawings.

The advantages, the features, and schemes of achieving the advantagesand features of the present invention will be apparently comprehended bythose skilled in the art based on the embodiments, which are detailedlater in detail, together with accompanying drawings. The presentinvention is not limited to the following embodiments but includesvarious applications and modifications. The embodiments will make thedisclosure of the present invention complete, and allow those skilled inthe art to completely comprehend the scope of the present invention. Thepresent invention is only defined within the scope of accompanyingclaims.

The same reference numerals denote the same elements throughout thespecification, and sizes, positions, and coupling relationships of theelements may be exaggerated for clarity.

According to the present invention, a reaction quantity of europium maybe increased and, at the same time, an electrowinning speed of theeuropium may be increased without using a stirring unit and a porouselectrode, without rotating an electrolytic bath and without performinga process of electrowinning several times.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic perspective view showing a channeled cellconstituting a device for electrowinning europium according to anembodiment of the present invention.

FIG. 2 is a schematic plan view showing a channeled cell constituting adevice for electrowinning europium according to an embodiment of thepresent invention.

FIG. 3 is a schematic sectional view showing a channeled cellconstituting a device for electrowinning europium according to anembodiment of the present invention.

FIG. 4 is a schematic sectional view showing a device for electrowinningeuropium according to an embodiment of the present invention.

FIGS. 5 a and 5 b are a view showing a simulation of a fluid flowdifference according to Reynolds number in a channel of a device forelectrowinning europium according to an embodiment of the presentinvention, where FIG. 5 a is a view showing a case that the Reynoldsnumber is 69.44 and FIG. 5 b is a view showing a case that the Reynoldsnumber is 6944.

FIG. 6 is a graph showing variations of Reynolds number and a recoveryrate in a device for electrowinning europium according to an embodimentof the present invention.

FIG. 7 is a graph showing a quantity of electric charge (which is avalue substituted into applied quantity of electric charge/theoreticalquantity of electric charge) and a recovery rate in a device forelectrowinning europium according to an embodiment of the presentinvention.

FIG. 8 is a graph showing variations of a channel length and a recoveryrate in a device for electrowinning europium according to an embodimentof the present invention.

FIG. 9 is a graph showing variations of a channel sectional area and arecovery rate in a device for electrowinning europium according to anembodiment of the present invention.

FIG. 10 is a graph showing variations of pH of a solution containingeuropium electrolytic Eu³⁺ and a recovery rate in a device forelectrowinning europium according to an embodiment of the presentinvention.

FIG. 11 is a flowchart schematically illustrating a method ofelectrowinning a rare metal according to an embodiment of the presentinvention.

FIG. 12 is a schematic view showing an Hg-cathode electrowinning deviceaccording to the related art.

FIG. 13 is schematic view showing an ion-exchange membrane electrolyticreduction device according to the related art.

FIG. 14 is a schematic view showing a porous carbon electrodeelectrolytic reduction device according to the related art.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter embodiments of the present invention will be described indetail with reference to accompanying drawings.

FIG. 1 is a schematic perspective view showing a channeled cellconstituting a device for electrowinning europium according to anembodiment of the present invention.

Referring to FIG. 1, a channeled cell 100 constituting a device forelectrowinning europium according to an embodiment of the presentinvention may include a substrate 120, a channel 160 including an inlet130 through which an electrowinning solution is input and an outlet 140through which an electrowinning completed solution is discharged, and aturbulent flow generating bead 180 formed at a part of the channel 160.

As shown in FIG. 1, although only one channeled cell 100 constituting acathode or anode of the device for electrowinning europium is depictedin FIG. 1, it should be understood that two channeled cells 100 arerequired for the cathode and anode. This will be described below withreference to FIG. 4.

As shown in FIG. 1, although the channel 160 of the channeled cell 100may have an arc shape, if required, the channel 160 may have a shapeformed by alternating a U-shape and an inverted-U shape. That is, thechannel 160 may include a bent portion having a curved shape.

Only, since the channel 160 depicted in FIG. 1 has the by-effect thatthe fluidity of the electrowinning solution, that is, the Reynoldsnumber is increased at the portion bent at a right angle, it ispreferable to allow the channel 160 to have the arc shape.

Preferably, the channeled cell 100 or the substrate 120 is formed ofgraphite.

The reason of forming the channeled cell 100 or the substrate 120 ofgraphite is because the graphite is not corroded by acid, does not reactwith the europium obtained through the electrowinning, has excellentworkability, and is a low price material.

As described above, it is preferable in the device for electrowinningeuropium to form the channeled cell 100 and the substrate 120 in thesame shape.

As will be described below with reference to FIG. 4, the channeled cell100 and the substrate 120 are preferably arranged to be matched witheach other.

Further, as shown in FIG. 1, at least one turbulent flow generating bead180 is preferably formed in the channel 160 provided on the substrate120 every a unit length.

The unit length will be described below with reference to FIG. 2.Further, the preferable turbulent flow generating bead 180 will bedescribed with reference to FIG. 3.

FIG. 2 is a plan view showing a channeled cell constituting a device forelectrowinning europium according to an embodiment of the presentinvention.

It may be understood that the channeled cell 200 constituting the devicefor electrowinning europium depicted in FIG. 2 substantially has thesame configuration as that depicted in FIG. 1. Thus, in the descriptionof FIG. 2, the same elements will be assigned with the same referencenumerals, and the repetition in the description of the same elementshaving the same reference numerals will be omitted in order to avoidredundancy.

As shown in FIG. 2, it may be known that the turbulent flow generatingbead 180 is formed at a central portion of the channeled cell 200 withrespect to a horizontal width.

In this case, it should be understood that the unit length representsthe length from left to right of each channel 160 shown in FIG. 2.

As shown in FIG. 2, although the channel 160 may be formed from left toright in a single unit 160, the channel 160 may be formed in two columnsseparated from each other in the channel cell 200 like a double-arcshape.

If the unit length of the channel 160 having the arc shape is equal to‘1’, the unit length of the channel 160 having the arc shape may beequal to ‘½’.

In this case, it is preferable to understand the unit length as asubstituted unit length.

Thus, when at least one turbulent flow generating bead 180 is formedevery the unit length in a case of the arc shape, at least one turbulentflow generating bead 180 may be formed every the unit length in a caseof the double-arc shape. When the number of turbulent flow generatingbeads 180 having the double arc shape is compared with that of turbulentflow generating beads 180 having the arc shape, the number of turbulentflow generating beads 180 having the double-arc shape may be two timesmore than the number of turbulent flow generating beads 180 having thearc shape.

FIG. 3 is a schematic sectional view showing a channeled cellconstituting a device for electrowinning europium according to anembodiment of the present invention.

In the channeled cell 300 constituting the device for electrowinningeuropium according to an embodiment of the present invention, asectional shape of the turbulent flow generating bead 180 formed on theinner surface of the channel 160 may be known from FIG. 3.

As shown in FIG. 3, the turbulent flow generating bead 180 substantiallyhas a cross-sectional surface of a trapezoid shape, but the sectionalshape of the turbulent flow generating bead 180 is not limited thereto.

For example, the turbulent flow generating bead 180 may have across-section surface of a hexagonal pillar, a water drop shape or asemicircular shape.

In short, preferably, the turbulent flow generating bead 180 protrudesfrom the inner surface of the channel 160 at a suitable height.

To the contrary, the turbulent flow generating bead 180 may be formed byallowing the inner surface of the channel 160 to be concaved.

That is, according to an embodiment of the present invention, the bead180 may be formed on the inner surface of the channel 160 in aconcave-convex shape.

The bead 180 may be alternately formed on the inner surface of thechannel 160.

It should be known that the bead 180 may have any shapes if the bead 180can cause turbulent flow on the inner surface of the channel 160.

As described above, the turbulent flow generating bead 180 may protrudefrom the inner surface of the channel 160. In this case, a height of theturbulent flow generating bead 180 may have preferably a half of theheight of the channel 160, or more preferably, two thirds of the heightof the channel 160.

Even when the bead 180 is formed by allowing the inner surface of thechannel 160 to be concaved, the height of the bead 180 is preferablydetermined in accordance with the above description.

A width or length of the turbulent flow generating bead 180 may be equalto that of the channel 160. However, the width of the turbulent flowgenerating bead 180, that is, the width, which is widened to the leftand right in a direction of the unit length based on the width, is notlimited to the width of the channel 160, but even when the width of theturbulent flow generating bead 180 is not smaller than that of thechannel 160, if the by-effect of turbulent flow generation, that is,stirring is obtained, the turbulent flow generating bead 180 may haveany widths.

The inlet 130 is depicted at a low end of FIG. 3. The reason is becauseit is assumed that the electrowinning solution is input from the rearsurface of the substrate 120 when an ion-exchange membrane 420 (see FIG.4) is finally interposed in the substrate 120.

Thus, it should be known that the shape of the inlet 130 may be changedinto another suitable shape.

Three turbulent flow generating beads 180 are depicted in FIG. 3. Asdescribed above, this means that three turbulent flow generating beads180 are formed per the unit length of the channel having.

That is, the turbulent flow generating bead 180 formed at one place inthe channel 160 having the unit length has the arc shape as shown inFIG. 2. However, in FIG. 3, the turbulent flow generating beads 180 areformed at three places per the unit length of the channel having.

FIG. 4 is a schematic sectional view showing a device for electrowinningeuropium according to an embodiment of the present invention.

It may be known from FIG. 4 that right and left substrates 120-1 and120-2 are tightly coupled to each other in the device 400 forelectrowinning europium according to an embodiment of the presentinvention in the state that the ion exchange membrane 420 is interposedbetween the right and left substrates 120-1 and 120-2.

It is preferably understood that the right and left substrates 120-1 and120-2 serve as a cathode cell and an anode cell. In the followingdescription, the cathode cell may be referred to as a cathode or asubstrate and the anode cell may be referred to as an anode or asubstrate. However, it should be noted that they represent the sameobjects.

It is the most preferable that the right and left substrates 120-1 and120-2, which serves as the anode and cathode cells, are formed ofgraphite.

The reason that the right and left substrates 120-1 and 120-2, all areformed of graphite has been described above.

It may be known from FIG. 4 that the cross-sectional shape of thechannel 160 is rectangular. However, as described above, the sectionalshape of the channel 160 may not be limited to the rectangular shape.

Meanwhile, it is preferable that the right and left substrates 120-1 and120-2 have the same shape as described above.

All of the channels 160 formed in the right and left substrates 120-1and 120-2 are arranged to match with each other.

In this case, the matched arrangement of both channels 160 means thatthe openings of both channels 160, which are formed in the right andleft substrates 120-1 and 120-2 and face each other about theion-exchange membrane 420, match with each other.

That is, when three channels 160 are formed in the right substrate120-1, three channels 160 are formed in the left substrate 120-2. Inaddition, the right and left substrates 120-1 and 120-2 are arrangedsuch that the openings of the channels 160 of one side are matched withthe openings of the channels 160 of the opposite side.

Next, the chemical reaction of Eu ion (Eu³⁺) caused in FIG. 4 will bedescribed.

The arrow {circle around (a)} of FIG. 4, which is depicted to describeone example of the rare metal electrowinning according to the presentinvention, represents that a solution containing Eu³⁺ is input into thecathode cell as an electrowinning solution. For example, the input ofthe electrowinning solution is preferably performed through the inlet130 of FIG. 1.

The solution containing Eu³⁺ refer to a solution that contains Eu³⁺among solutions which are obtained by removing light rare earth elementsfrom solutions, in which the rear earth element is leached, through asolvent extraction.

The Eu³⁺ contained in the solution containing Eu³⁺ is reduced toeuropium through the sequential reactions of following chemical reactionformulas 1 and 2

Eu³⁺ +e ⁻→Eu²⁺  [Chemical Reaction Formula 1]

Eu²⁺+SO₄ ²⁻→EuSO₄(s)↓  [Chemical Reaction Formula 2]

Since the reduction of europium occurs on the electrode surface duringthe reduction reaction through the electrowinning expressed as thechemical reaction formula 1, in the related art, a scheme of increasinga reaction surface area using a porous electrode (see FIGS. 13 and 14)is utilized to improve the reaction efficiency.

To the contrary, it should be noted that the electrowinning is performedby using the configuration of the substrates 120-1 and 120-2, thechannels 160 formed in the substrates 120-1 and 120-2, and the turbulentflow generating bead 180 formed in at least one part of the channels 160in the present invention as shown in FIGS. 1 to 4.

Preferably, as soon as the Eu³⁺-containing solution is input in thedirection of arrow {circle around (a)}, for example, a Fe²⁺-containingsolution, which can cause a pair reaction, is input in the direction ofarrow {circle around (c)}.

In this case, the pair reaction represents a reaction that can cause themost suitable reaction of reducing Eu³⁺ contained in the Eu³⁺-containingsolution to Eu²⁺. In the present invention, the Fe²⁺-containing solutionis used for the pair reaction.

While the Fe²⁺-containing solution is flowing from the allow {circlearound (c)} to the arrow {circle around (d)}, the Fe²⁺-containingsolution makes the pair reaction with the Eu³⁺-containing solution.

As the result, the Fe^(2÷)-containing solution is oxidized by theEu³⁺-containing solution. In this case, while the Fe²⁺ is oxidized intoFe³⁺, an electron (e⁻) generated from the left substrate 120-2 flowsinto the right substrate 120-1 electrically connected thereto through acurrent flow (not shown), so that the Eu³⁺ in the Eu³⁺-containingsolution input in the direction of arrow {circle around (a)} is reducedto Eu²⁺ by the electron (e⁻).

It should be understood that the reduction of Eu³⁺ in theEu³⁺-containing solution to Eu²⁺ occurs not only on a part of thesurface of the right substrate 120-1, but also actually on the remainingthree surfaces of the channel 160 except for a part making contact withthe ion-exchange membrane 420 at the same time.

The detailed mechanism of simultaneously causing the reduction of Eu³⁺in the Eu³⁺-containing solution to Eu²⁺ on the three surfaces of thechannel 160 will be described with reference to FIGS. 5 a and 5 b.

Only, it is preferable to understand that the reason of simultaneouslycausing the reduction of Eu³⁺ in the Eu³⁺-containing solution to Eu²⁺ onthe three surfaces of the channel 160 is because the Eu³⁺-containingsolution flows at Reynolds number of 2000 or more so that a turbulentflow is generated.

For reference, it should be noted that the Eu³⁺-containing solution asthe electrowinning solution flows in the direction perpendicular to theground, that is, in the y-axis direction perpendicular to the groundwhen it is assumed that the ground is an x-axis.

The remaining Eu³⁺-containing solution after being reduced to Eu²⁺ maybe discharged through the outlet 140 denoted as arrow {circle around(b)} in FIG. 4.

In FIG. 4, while the Eu³⁺-containing solution flows from the arrow{circle around (a)} to the arrow {circle around (b)}, most Eu³⁺ isreduced to Eu²⁺. This is because current flows into the ion-exchangemembrane 420 formed between the right and left substrates 120-1 and120-2 so that the current helps most Eu³⁺ to be reduced to Eu²⁺ whilethe Eu³⁺-containing solution flows.

In this case, it is preferable that Cl⁻ ions exist in the ion-exchangemembrane 420, so that the reduction of Eu³⁺ to Eu²⁺ is accelerated byCl⁻ ions.

It has been already described above that the oxidation of Fe²⁺ to Fe³⁺as the pair reaction corresponding to the reduction of Eu³⁺ to Eu²⁺occurs on the left substrate 120-2 while the reduction of Eu³⁺ to Eu²⁺occurs on the right substrate 120-1.

The solution containing Eu²⁺ reduced from Eu³⁺, that is, theEu²⁺-containing solution is discharged in the direction of arrow {circlearound (b)} and then, may be collected in the europium reactioncontainer 440 containing a H₂SO₄ solution previously prepared.

The reaction of Eu²⁺ and SO₄ ²⁻ ions in the europium reaction container440 may be expressed as the chemical reaction formula 2 of Eu²⁺+SO₄²⁻→EuSO₄(s)↓.

Finally, it should be noted that although the europium is selectivelyprecipitated as EuSO₄ precipitation, other rare earth element ions(Sm³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Y³⁺, etc.) react with sulfuric acid (H₂SO₄) sothat other rare earth elements are not precipitated but continuouslyexist in an ion state.

FIGS. 5 a and 5 b are a view showing a simulation of a fluid flowdifference according to Reynolds number in a channel of a device forelectrowinning europium according to an embodiment of the presentinvention, where FIG. 5 a is a view showing a case that the Reynoldsnumber is 69.44 and FIG. 5 b is a view showing a case that the Reynoldsnumber is 6944.

In more detail, FIG. 5 a is a view showing the case that the Reynoldsnumber of 69.44 and the flow rate of 10 cc/hr, and FIG. 5 b is a viewshowing the case of the Reynolds number of 6944 and the flow rate of1000 cc/hr.

Specifically, FIGS. 5 a and 5 b are views showing the mass-transferphenomenon according to each of the Reynolds (Re) numbers as velocityvectors colored according to velocity magnitudes when the electrowinningsolution is provided into the channel 160.

It may be known from FIG. 5 a that, when the Re number is low, most ofthe mass migrations occur at the central portion of the channel 160,that is, only a portion colored with yellow. Specifically, the massmigration occurs only in the y-axis direction and rarely occurs in thex-z axis direction.

To the contrary, It may be known from FIG. 5 b that, when the Re numberis high, the mass migration actively occur in the x-z axis directions.The above phenomenon may occur because the electrowinning solution inputthrough the inlet 130 forms swirl and the swirl continuously flows inthe y-axis direction.

It is known in the art that the swirl actually occurs in a turbulentflow state and the swirl phenomenon due to the turbulent flow iseffectively generated at the Re number 2000.

Hereinafter, ‘Re number’ will be described in brief.

The Reynolds number is a term of the hydrodynamic field that is definedas the ratio of “an inertia force” to “a viscous force”. In detail, theRe number is defined as the simple formula of (liquid density*flowvelocity*vertical height)/liquid viscosity.

The Re number is utilized as one of the most important non-dimensionalnumbers in hydrodynamics and specifically, hydrokinetics. It has beenknow that, when the Re numbers are similar with each other, two types offluid flows represent flows that are similar to each other inhydrodynamics.

When the Re number is low, a laminar flow dominated by a viscous force,which is calm and has a constant fluid flow, is generated. To thecontrary, When the Re number is high, a turbulent flow dominated by aninertial force, which includes a vortex and has extreme perturbations,is generated.

Meanwhile, the Re number is named after Osborne Reynolds(1842-1912).

As described above, it should be understood that the case of the Renumber of 2000 or more is noted in the present invention.

When the Re number is 2000 or more, it may be expected that since aflowing material, for example, an electrowinning solution makes contactwith the electrode surface, and in more detail, makes contact with x andy axes, the probability that the flowing material makes contact with theelectrode surface is increased, so that the reaction efficiency isproportionally increased.

To the contrary, when the Re number is less than 2000, it may beexpected that although the flowing material, for example, anelectrowinning solution makes contact with the electrode surface, theprobability that the flowing material makes contact with the electrodesurface is decreased, so that the reaction efficiency is proportionallydecreased.

Hereinafter, various examples of the device for electrowinning europiumaccording to the embodiment of the present invention will be described.

First, as described above, the solution containing Eu³⁺ refers to asolution that contains Eu³⁺ among solutions which are obtained byremoving light rare earth elements from solutions, in which the rearearth element is leached, through a solvent extraction. In this case,although the pH value of the Eu³⁺-containing solution is about 0.5, itshould be noted that the Eu³⁺-containing solution may have a pH value inthe range −1 to 4 under various situations. However, it should be notedthat the solution having 0.5 pH has been used in the present invention.

The composition of the Eu³⁺-containing solution used in the specificembodiment of the present invention is as following Table 1.

TABLE 1 Element Concentration (ppm) Sm 9094 Eu 2000 Gd 15372 Tb 913 Dy732 Y 1368

It may be understood based on Table 1 that the concentration of Eucontained in the Eu³⁺-containing solution is 2000 ppm.

Meanwhile, a rectangular shape has been applied as the cross sectionalshape of the channel.

The cross sectional areas of the channel have been set into 0.2, 0.5 and1.0 cm².

The lengths of the channel have been formed at 10, 50, 100, and 200 cm,respectively. In these cases, the cross sectional areas have been fixedto 0.2 cm² for convenience.

The theoretical quantity of electric charge required for reducing Eu³⁺ions to 100% may be calculated according to Faraday law. It has been setin the present invention to apply 90%, 100%, 150% and 200% of thetheoretical quantity of electric charge.

As described above, it is preferable to prepare the H₂SO₄ solution forprecipitating EuSO₄ in the europium reaction container 440 (see FIG. 4).In this case, it is preferable to satisfy the interaction formula [SO₄²⁻]/[Eu³⁺]=1˜5. In the present invention, the quantity of SO₄ ²⁻ ions ismaintained to be two times the quantity of europium.

Further, in the present invention, the recovery rate is obtained bymeasuring the quantity of Eu residual in the solution using the ICP-AES(Inductively Coupled Plasma-Atomic Emission Spectrometer) aftersolid-liquid separating the EuSO₄ precipitates.

Meanwhile, based on various kinds of basic conditions described above,the experiments have been performed under following various differentconditions: {circle around (1)} Re number (see FIG. 6), {circle around(2)} Quantity of electric charge, {circle around (3)} channel length(see FIG. 8), {circle around (4)} Cross-sectional area of channel (seeFIG. 9), {circle around (5)} pH of Eu³⁺-containing solution (see FIG.10). Hereinafter, the recovery rates (%) under the above various kindsof electrolytic condition will be described.

First, the recovery rate according to the Re number will be described.

FIG. 6 is a graph showing variations of Reynolds number and a recoveryrate in a device for electrowinning europium according to an embodimentof the present invention.

In FIG. 6, various kinds of variable control conditions are the same asthose in following Table 2.

TABLE 2 Cross-sectional Channel Quantity of area of channel length [SO₄²⁻]/ applied electric pH (cm²) (cm) [Eu³⁺] charge (%) 0.5 0.2 100 2 150

According to the experimental result of the europium reduction performedbased on the variable conditions in Table 2, the recovery rate (%)exceeds about 60% at the Re number less than 2,000, that is, about theRe number of 1,500. However, it is known that the recovery rate (%)reaches at 95% at the Re number of 2,000 or more so that the recoveryrate actually approaches to 100%.

Meanwhile, even though the Re number reaches at 3,000, there is nodifference in the recovery rate. Thus, it is understood that the Renumber of at least 2,000 according to an embodiment of the presentinvention is preferable.

Next, the recovery rate according to the quantity of electric chargewill be described.

FIG. 7 is a graph showing a quantity of electric charge (which is avalue substituted into applied quantity of electric charge/theoreticalquantity of electric charge) and a recovery rate in a device forelectrowinning europium according to an embodiment of the presentinvention.

In FIG. 7, various kinds of variable control conditions are the same asthose in following Table 3.

TABLE 3 Cross-sectional Channel area of channel length [SO₄ ²⁻]/ Re pH(cm²) (cm) [Eu³⁺] number 0.5 0.2 100 2 2082

According to the experimental result of the europium reduction performedbased on the variable conditions in Table 3, as shown in FIG. 7, whenthe ratio of the substituted value of the quantity of applied electriccharge into the theoretical quantity of electric charge, that is, thequantity of electric charge is 90%, the recovery rate (%) is less than70%. However, when the quantity of electric charge is 110% or more, therecovery rate (%) are about 90% in all cases. Thus, when the quantity ofsupplied electric charge is over 110%, the quantity of electric chargehas no correlation with the recovery rate (%).

Next, the recovery rate according to the channel length will bedescribed.

FIG. 8 is a graph showing variations of a channel length and a recoveryrate in a device for electrowinning europium according to an embodimentof the present invention.

In FIG. 8, various kinds of variable control conditions are the same asthose of following Table 4.

TABLE 4 Cross sectional Quantity of area of channel applied electric[SO₄ ²⁻]/ Re pH (cm²) charge (%) [Eu³⁺] number 0.5 0.2 150 2 2082

Since the contact time and contact area are increased as the channellength is increased, it is expected that the reaction efficiency ofeuropium electrowinning may be remarkably improved. Based on the abovefact, the recovery rate will be described with reference to Table 4 andFIG. 8.

According to the experimental result of the europium reduction performedbased on the variable conditions in Table 4, as shown in FIG. 8, in therelationship between the channel length and the recovery rate (%), therecovery rate (%) is not increased proportionally to the channel length.

In more detail, when the channel length is about 50 cm, the recoveryrate (%) is about 88%. However, when the channel length is 100 cm, therecovery rate (%) is increased to 93%. When the channel length islengthened to 200 cm, against expectations, the recovery rate (%) is notmore increased.

Next, the recovery rate according to the cross-sectional area of thechannel will be described.

FIG. 9 is a graph showing variations of a channel sectional area and arecovery rate in a device for electrowinning europium according to anembodiment of the present invention.

In FIG. 9, various kinds of variable control conditions are the same asthose in following Table 5.

TABLE 5 Channel Quantity of length applied electric [SO₄ ²⁻]/ Re pH (cm)charge (%) [Eu³⁺] number 0.5 100 150 2 2082

It will be first mentioned that the quantity of flowing fluid must bemore increased to maintain a constant Re number when the cross-sectionalarea of channel is increased.

As the result of the europium reduction according to the variableconditions in Table 5, as shown in FIG. 9, when the cross-sectional areaof channel is 0.2 cm², 0.5 cm² or even 1.0 cm², the recovery rate is notalmost changed.

This means that the cross sectional area of channel does not exertinfluence on the recovery rate when the Re number is 2,000 or more.

Next, the recovery rate and pH of the Eu³⁺-containing solution will bedescribed.

FIG. 10 is a graph showing variations of the pH of the Eu³⁺-containingsolution and the recovery rate in a device for electrowinning europiumaccording to an embodiment of the present invention.

In FIG. 10, various kinds of variable control conditions are the same asthose in following Table 6.

TABLE 6 Channel Quantity of Cross-sectional length applied electric [SO₄²⁻]/ Re area of channel (cm) charge (%) [Eu³⁺] number 0.2 100 110 2 2082

First, it has been expected that since an H₂ discharging voltage islowered when the pH is increased, the efficiency of the Eu³⁺ reducingreaction is increased.

As the result of the europium reduction according to the variableconditions in Table 6, as shown in FIG. 10, the recovery rate (%) issomewhat increased as the pH is increased. However, since it is obviousthat high recovery rates (%) are actually obtained in most of pH values,this means that the variation of a pH value is not very important whenreducing europium.

Hereinafter, a method of electrowinning europium according to anembodiment of the present invention will be described.

FIG. 11 is a flowchart schematically illustrating a method ofelectrowinning a rare metal according to an embodiment of the presentinvention.

Referring to FIG. 11, a method of electrowinning europium according toan embodiment of the present includes a step S10 of preparingsubstrates, a step S20 of forming channels in the substrates, a step S30of attaching the substrates to both side surfaces of an ion-exchangemembrane, a step S40 of electrowinning europium after inputting anEu³⁺-containing solution, and a step S50 of reacting electrolyzedEu³⁺-containing solution with H₂SO₄ solution to obtain EuSO₄precipitation.

Step of Preparing Substrate

As described with reference to FIG. 1, in the step S10 of preparingsubstrates, the substrates 120 including graphite are prepared.

In this case, as described above, two substrates 120-1 and 120-2 for acathode and an anode are prepared.

Step of Forming Channel in Substrate

As described with reference to FIGS. 1 to 3, in the step S20 of formingchannels in the substrates, the channels 160 having a particular shapeare formed in the substrates 120-1 and 120-2.

In this case, although the description of the various kinds ofconditions about the channel 160 will be omitted since the various kindsof conditions about the channel 160 has been described above, it shouldbe noted that at least one turbulent flow generating bead 180 must beformed in the channels every a unit length.

Step of Attaching Substrates to Both Side Surfaces of Ion-ExchangeMembrane

In the step S30 of attaching the substrates to both side surfaces of theion-exchange membrane, the substrate 120-1 and 120-2 for a cathode andan anode are attached to both side surfaces of the ion exchange membrane420 (see FIG. 4).

In the present invention, a negative ion exchange membrane has been usedas the ion exchange membrane 420 because an Eu³⁺-containing solution hasbeen used as the electrowinning solution.

Step of Electrowinning Europium after Inputting Eu³⁺-Containing Solution

In the step S40 of electrowinning europium after inputting anEu³⁺-containing solution, as described above, the Eu³⁺-containingsolution is input through the inlet 130 and then the electrowinning isperformed.

In this case, as shown in FIGS. 5 a and 5 b, the Eu³⁺-containingsolution flows at the Re number of 2,000 by the turbulent flowgenerating bead 180 formed in the substrate 120-1, so that theEu³⁺-containing solution is electrolyzed on the three surfaces of thechannel 160 to reduce Eu³⁺ to Eu²⁺.

Although the Re number of 2,000 or more is achieved by inputting theEu³⁺-containing solution into the inlet 130 at a high rate, it should benoted that the Re number of 2,000 or more may be achieved through theturbulent flow generating bead 180.

Step of Reacting Electrolyzed Eu³⁺-Containing Solution with H₂SO₄Solution to Obtain EuSO₄ Precipitation

Finally, in the step S50 of reacting the electrolyzed Eu^(3÷)-containingsolution with H₂SO₄ solution to obtain EuSO₄ precipitation, theEu²⁺-containing solution reduced in the step S40 is collected in theeuropium reaction container 440 and then, the Eu²⁺-containing solutionreacts with the sulfuric acid (H₂SO₄) contained in the europium reactioncontainer 440, so that the EuSO₄ is finally obtained.

The detailed chemical reaction formula has been described with referenceto the Chemical reaction formula 2, and the reaction process has beendescribed with reference to FIG. 4.

Although the present invention has been described by making reference tothe embodiments and accompanying drawings, it should be understood thatthe present invention is not limited to the embodiments but includes allmodifications, equivalents and alternatives. Accordingly, those skilledin the art should understand the spirit and scope of the presentinvention as defined in the following claims. In addition, those skilledin the art should understand that the equivalents and the modificationsbelong to the scope of the spirit of the present invention.

What is claimed is:
 1. A device for electrowinning europium using achanneled cell, the device comprising: a cathode cell including achannel having an inlet and an outlet; an anode cell including a channelhaving an inlet and an outlet; and an ion-exchange membrane tightlyinterposed between the cathode and anode cells, wherein reduced europiumis exhausted from the outlet of the cathode cell.
 2. The device of claim1, wherein at least one bead for generating a turbulent flow is formedon each inner surface of the channels of the cathode and anode cells. 3.The device of claim 1, wherein a quantity of electric charge applied tothe cathode and anode cells is 110% or more when the quantity ofelectric charge is substituted into a value obtained by dividing aquantity of applied electric charge by a theoretical quantity ofelectric charge.
 4. The device of claim 1, wherein the cathode and anodecells include graphite.
 5. The device of claim 1, wherein a sectionalshape of the channel is one of a rectangular shape, a U-shape, and aV-shape.
 6. The device of claim 1, wherein an electrowinning solutioninput to the inlet flows at Reynolds number of 2000 or more.
 7. Thedevice of claim 1, wherein a solution containing Eu³⁺ is input to theinlet of the cathode cell, and a solution containing Fe²⁺, which is ableto p-react with the solution containing Eu³⁺ input to the cathode cell,is input to the inlet of the anode cell.
 8. The device of claim 2,wherein at least one bead for generating the turbulent flow is installedper a unit length of the channel.
 9. A method of electrowinning europiumusing a channeled cell, the method comprising: preparing a substrate fora cathode cell and a substrate for an anode cell; forming channels inthe substrates; fixing the substrates having the channels to both sidesof an ion-exchange membrane by closely attaching the substrates to bothsides of the ion-exchange membrane; and electrowinning europium afterinputting a solution containing an europium ion through an inlet formedin the substrate.
 10. The method of claim 9, wherein the substrateincludes graphite.
 11. The method of claim 9, wherein at least one beadfor generating turbulent flow is formed on an inner surface of thechannel of the substrate.
 12. The method of claim 9, wherein anelectrowinning solution input to the inlet flows at Reynolds number of2000 or more.